Flashcards in General Physiology First Aid Extra Info Deck (32)
Formula for determining Physiologic dead space
Taco Paco Peco Paco
Vt = Tidal Volume
PaCO2 = arterial PCO2
PECO2 = expired air PCO2
Vd = Physiologic dead space
Vd = Vt x (PaCO2 - PECO2)/(PaCO2)
Minute Ventilation (VE)
Total volume of gas entering the lungs per minute
VE = Vt x RR
RR = Respiratory Rate
Alveolar Ventilation (VA)
Volume of gas per unit time that reaches the alveoli
VA = (Vt - Vd) x RR
There is a tendency for the lungs to ________ and for the chest wall to _____.
Lungs to collapse inward and the chest wall to spring outward
At the FRC, what are the pressures of the lungs?
Inward pull of the lung is balanced by outward pull of chest wall and system pressure is atmospheric
At FRC, airway and alveolar pressures are ____ and intrapleural pressure is ____ which prevents _____.
____ is at a minimum.
Zero, negative, pneumothorax, PVR
2 forms of the hemoglobin chains
T = Taut form - Has low affinity for O2
R = Relaxed form - Has high affinity for O2 (300x)
What favors the taut form of hemoglobin?
Increased Cl, H+, CO2, 2,3-BPG, and temperature since these shift the dissociation curve to the right, leading to increased O2 unloading
Why does fetal hemoglobin have higher affinity for O2 and what are the chain type differences
Fetal Hb is made of 2a and 2y chains. This causes fetal hemoglobin to have a lower affinity for 2,3-BPG than adult Hb, and thus has higher affinity for O2.
When is hemoglobin taut vs. relaxed?
Taut in Tissues
Relaxed in Respiratory tract
What is methemoglobin?
Oxidized form of Hb (ferric, Fe3+) that does not bind O2 as readily, but has increased affinity for cyanide (iron in Hb usually is in a reduced state of Fe2+)
How does methemoglobinemia present?
Cyanosis and chocolate colored blood
How do you treat cyanide poisoning?
Use nitrites to oxidize Hb to methemoglobin, which binds cyanide. Use thiosulfate to bind this cyanide, forming thiocyanate, which is renally excreted
Treatment of methemoglobinemia can be treated with what?
Nitrites cause poisoning by____________.
oxidizing Fe2+ to Fe3+
What is carboxyhemoglobin and what does it do to normal hemoglobin?
CO bound to Hemoglobin which shifts the dissociation curve to the left due to a decreased O2 binding capacity, causing a decreased O2 unloading in tissues.
What is PVR?
Pulmonary Vascular Resistance
PVR = (Pressure in pulmonary artery - Pulmonary wedge pressure or pressure in the left atrium) / Cardiac output
What is the alveolar gas equation?
PAO2 = PIO2 - (PaCO2/R)
PIO2 = PO2 of inspired air
PaCO2 = arterial PCO2
R = respiratory quotient = CO2 produced/O2 consumed
We can also just do:
150 - PaCO2/0.8
Calculate A-a gradient
PAO2 - PaO2 = 10-15mmHg
When might we see an increased A-a gradient?
May occur in hypoxemia, causes include shunting, V/Q mismatch, fibrosis (impairs diffusion)
When we have Hypoxemia but a normal A-a gradient, what could be the cause?
High altitude or hypoventilation
When we have hypoxemia but an increased A-a gradient, what could be the cause?
V/Q mismatch, diffusion limitations, right to left shunt
Causes of hypoxia
Decreased Cardiac output
Causes of ischemia or loss of blood flow
Impeded arterial flow or a decreased venous drainage
Ideal situation for V/Q?
V/Q = 1 which would indicate ventilationm atching perfusion for adequate gas exchange
V/Q for the apex and what is indicates
= 3, which means wasted ventilation
V/Q for the base of the lung and what it indicates
= 0.6 and indicates wasted perfusion
What is true about ventilation and perfusion at the base of the lung?
They are both greatest there than at the apex
With exercise there is _____ in apical capillaries resulting in a V/Q ratio that approaches ______.
Vasodilation, approaches 1